'The Lily Pond' printed from http://nrich.maths.org/

Once there was a rectangular lily pond. In it there were $12$
lily leaves and $6$ lily flowers.

Freddie the Frog lived on one lily leaf which we will call "leaf
$1$, row $4$". Sammy Snail lived on another leaf which we will call
"leaf $2$, row $3$". Freddie used to jump from leaf to leaf but he
did not like jumping over the lily flowers so he never jumped
diagonally.

One day Freddie went to see Sammy Snail. He visited as many of
the leaves as he could on the way but only visited each leaf once.
Which was the best way for him to go?

If Sammy lived on a different leaf Freddie would be able to go
on every leaf on his way to see Sammy. Which leaves would make this
possible?